Lubrication fluids are typically applied to moving surfaces to reduce friction between surfaces, thereby improving efficiency and reducing wear. Lubrication fluids are also typically used to dissipate heat generated by the moving surfaces. One type of lubrication fluid is a petroleum-based lubrication oil. Such lubrication oil is typically used for internal combustion engines. Lubrication oils contain additives that help the lubrication oil to have a certain viscosity at a given temperature.
In general, the viscosity of lubrication oils and fluids are inversely dependent upon temperature. When the temperature of lubrication fluids is increased, the viscosity of such fluids generally decreases, and when the temperature is decreased, the viscosity of such fluids generally increases. For internal combustion engines, it is desirable to have lower viscosity at low temperatures to facilitate engine starting during cold weather, and a higher viscosity at higher ambient temperatures when lubrication properties typically decline.
Additives for such lubrication fluids and oils include rheology modifiers, including viscosity index (VI) improvers. Components of VI improvers derived from ethylene-alpha-olefin copolymers modify the rheological behavior to increase the lubricant viscosity and promote a more constant viscosity over a wider range of temperatures. Such VI improvers with higher ethylene contents can improve oil thickening (TE) and shear stability, as measured by shear stability index (“SSI”). Higher ethylene content VI improvers, however, tend to flocculate or aggregate in oil formulations leading to highly viscous, flocculated materials that precipitate out of the lubrication fluid. These precipitates are apparent as regions (e.g., “lumps”) of high viscosity or essentially complete solidification (e.g., “gels”) and can lead to clogs and blockages of pumps and other passageways for the lubrication fluid and can lead to harm and in some causes failure of moving machinery.
Blends of amorphous and semi-crystalline ethylene-based copolymers have been used to overcome or mitigate the propensity towards the formation of high viscosity flocculated materials. See, e.g., U.S. Pat. Nos. 7,402,235 and 5,391,617, and European Patent No. 0 638 611, the disclosures of which are incorporated herein by reference. There remains a need, however, for new rheology modifier compositions made from ethylene that are suitable for use in VI improvers that have high TE and good low temperature solution rheology properties.